1. Field of the Invention
The invention herein relates to an apparatus for treating domestic waste and sewage produced in residential dwellings.
2. Description of the Prior Art
A typical residential dwelling contains plumbing systems for providing water service and removal of domestic and other aqueous waste. In more urban areas, the waste system connects with a sewer main located outside the dwelling, usually under the fronting public road, which directs the discharged domestic waste to a centralized municipal waste treatment plant. In rural areas, however, a sewer main may not be conveniently available and a waste system usually must be provided on-site for treating and disposing of domestic waste.
Domestic waste produced from residential dwellings typically is comprised of a mixture of waste solids and water in varying proportions. In on-site systems, the disposal system water is separated from organics solids, which may include human, kitchen, laundry and other wastes, and is discharged to the local environment. The separated solids are treated and decomposed within the on-site system to varying extents and any residual remaining thereafter must be hauled elsewhere for ultimate disposal, such as at a municipal land fill or municipal waste treatment plant.
A variety of devices and apparatus are available for collecting and treating on-site domestic waste and sewage emanating from a residential dwelling. The most common of these decentralized treatment systems are septic treatment systems. These typically involve a septic tank which receives the domestic waste water influent from the residential building. The waste is held quiescently in the tank, permitting most of the solids to settle in the bottom of the tank. The partially clarified water may then be discharged onto the surrounding property. However, the water effluent still contains some dissolved and entrained solids, and is not sufficiently safe to discharge to surface waters. Typically, the water effluent is discharged to a leach field, where the water effluent is routed to a field of buried permeable pipes. The water effluent permeates through the walls of the pipes and into the surrounding subsoil. Any waste remaining in the water effluent is entrained in the surrounding subsoil and gradually decomposed by indigenous soil organisms. The water effluent percolates downward, eventually joining the local ground water table.
This means of discharge significantly constrains septic systems. Leach fields can be practically implemented only where the soil is sufficiently permeable to permit the water effluent to percolate through it. Shallow soils, i.e., thin soil layers with bedrock close to the surface, or soils with high clay contents often are not sufficiently permeable and are unsuitable for a septic tank system.
Within the septic tank, the waste solids gradually accumulate at the bottom. Anaerobic bacteria, naturally present in the waste, begin to decompose the waste solids. However, anaerobic bacteria are comparatively inefficient and can decompose only a small fraction of the waste solids. This results in a gradual accumulation of partially-treated solids within the bottom of the septic tank. These solids are still potentially pathogenetic and usually must be hauled to a municipal waste treatment plant for further treatment and ultimate disposal before the working volume of the septic tank has filled with solids.
Another on-site decentralized domestic waste treatment system is an aerobic, activated sludge process. The process is typically comprised of an apparatus with two chambers. The first chamber contains a mixed aqueous slurry of active aerobic bacteria, called activated sludge. Aerobic conditions are maintained in the activated sludge by injecting air by one of several means known in the art. The domestic waste influent is added into and mixed with activated sludge. Aerobic bacteria absorb and decompose the entrained and dissolved solids in the domestic waste.
A small purge stream exits from the first chamber into a second chamber with quiescent conditions. The sludge mass in the slurry settles to the bottom of the second chamber, while the separated water exits from it. Activated sludge solids settle faster than the raw solids in domestic waste, so the aqueous effluent from an aerobic treatment apparatus is usually clarified sufficiently to discharge directly to a surface water body. The settled sludge is also non-pathogenic and can be more easily discarded, such as by land-farming.
The aerobic process is more efficient than the anaerobic process, but has a higher initial cost because of the need for powered machinery to operate the aeration process, as well as a higher operating cost for the electrical power needed for the aeration machinery as well as maintenance costs for the machinery.
Another class of apparatus for treating domestic waste is composting toilets and waste composting units. These units treat domestic wastes by composting, which is a method of decaying organic solids with aerobic bacteria in a solid mass or pile, with little free excess water, rather than in a slurry or fluid system. In a composting system, the waste pile, being substantially devoid of excess free water, has many miniscule voids or pores through which air can circulate, bringing oxygen to the aerobic organisms in the central volumes of the waste pile. The aerobic organisms in the waste pile digest and metabolize the waste, reducing its volume and producing more environmentally compatible humus as a final waste product, which can be more easily disposed of.
For example, Ylösjoki, U.S. Pat. No. 5,171,690, is drawn to a composting device for kitchen and toilet waste, comprised of a multi-chambered bin having a permeable floor, and air space under the floor, and a vent stack in the top surface of the bin. Wastes are deposited into one of the chambers in the bin, and air circulates up through the waste pile and out the vent stack. Any excess free water in the waste pile can drain through the permeable floor.
Similarly, Sundberg, U.S. Pat. No. 3,840,907 and Clark, U.S. Pat. No. 4,096,592, are drawn to composting toilets with permeable floors and vent stacks, allowing vertical circulation of air for promoting the growth of aerobic bacteria.
These and similar composting systems provide an efficient and lower cost alternative to septic tank and activated sludge plants, but have several disadvantages.
In each case, only solid (moist) waste can be accepted in these composting toilets. A slurry discharge, such as from traditional toilets and water closets, would wash waste solids through the permeable floor and would render the remaining saturated wastes septic. This limitation thus necessitates the composting unit to be located in or directly adjacent to the residential dwelling separated from the traditional drain plumbing. Many people find a composting unit containing decaying human waste within or immediately adjacent to the household very objectionable offensive.
A composting unit would also not be suitable for other wastes that are discharged in a slurry, such as from kitchen sink drains, dishwasher and laundry washing machines. This would then necessary alterations in a dwelling's draining plumbing system, necessitating dual discharge systems.